1. Field of the Invention
The present invention relates to a fuel cell.
2. Discussion of the Background
For example, a solid polymer electrolyte fuel cell includes a unit cell, in which an electrolyte membrane-electrode assembly (MEA) is sandwiched between a pair of separators, the electrolyte membrane-electrode assembly having a polymer electrolyte membrane formed of a polymer ion exchange membrane, and the anode-side and cathode-side electrodes that are disposed on the both sides of the polymer electrolyte membrane. In this type of fuel cell, normally, a fuel cell stack, in which a predetermined number of unit cells are stacked together, is used as an in-vehicle fuel cell stack or the like.
In the above-described fuel cell, a fuel gas passage (reactant gas passage) for passing a fuel gas, which faces the anode-side electrode is formed in the surface of one separator, while an oxidant gas passage (reactant gas passage) for passing an oxidant gas, which faces the cathode-side electrode is formed in the surface of the other separator. In addition, a cooling medium passage for passing a cooling medium is provided between the separators along the surface direction of the separators.
Furthermore, in many cases, this type of fuel cell constitutes what is called an internal manifold type fuel cell that includes therein a fuel gas inlet communication hole (reactant gas communication hole) and a fuel gas outlet communication hole (reactant gas communication hole) that allow a fuel gas to flow in the stacking direction of the unit cells, an oxidant gas inlet communication hole (reactant gas communication hole) and an oxidant gas outlet communication hole (reactant gas communication hole) that allow an oxidant gas to flow, and a cooling medium inlet communication hole and a cooling medium outlet communication hole that allow a cooling medium to flow.
In this case, the reactant gas passage and the reactant gas communication hole communicate with each other via a connecting passage having parallel grooves in order to pass the reactant gas smoothly and uniformly. However, there is a problem in that when the separators and the membrane electrode assembly are tightened and secured together by interposing a sealing member therebetween, the sealing member enters the connecting passage, and thus a desired sealing function may not be maintained, and also, the reactant gas does not flow smoothly.
For example, in the solid polymer electrolyte fuel cell stack disclosed in Japanese Unexamined Patent Application Publication No. 2001-266911, a reactant gas passage which meanders on the surface of a separator 1, for example, an oxidant gas passage 2 is formed as illustrated in FIG. 13. The oxidant gas passage 2 communicates with an oxidant gas supply through hole 3 and an oxidant gas discharge through hole 4 that extend through a peripheral portion of the separator 1 in the stacking direction. Packing 5 is disposed in the separator 1 to allow the through holes 3, 4 to communicate with the oxidant gas passage 2 on the surface of the separator 1, while sealing other through holes from the through holes 3, 4 and the oxidant gas passage 2.
In the connecting passages 6a, 6b that respectively allow the through holes 3, 4 to communicate with the oxidant gas passage 2, SUS plates 7 as sealing members are disposed so as to cover the connecting passages 6a and 6b, respectively. The SUS (stainless steel) plates 7 are each formed in a rectangular shape, and are provided with ear portions 7a and 7b at two locations, respectively. The ear portions 7a, 7b are fitted into respective steped portions 8 that are formed in the separator 1.
In this manner, Japanese Unexamined Patent Application Publication No. 2001-266911 claims that a desired sealing function may be secured and may prevent an increase in the pressure loss of the reactant gas because the SUS plates 7 cover the connecting passages 6a, 6b, and thus a polymer electrolyte membrane (not shown) and the packing 5 do not fall into the oxidant gas passage 2.